Transition metal catalysis has solved countless problems in total synthesis, pharmaceutical chemistry, and the production of fine chemicals. While these reactions have traditionally been performed using platinum group metals (PGMs), there has been a recent push to develop methods that circumvent the need for expensive and toxic precious metal catalysts. A growing body of research has demonstrated that iron can be an excellent catalyst across a wide variety of organic transformations, including reactions that have proven difficult for PGMs, such as the cross-coupling of alkyl halides and Grignard reagents with both high activity and selectivity. While iron-catalyzed C-C cross-couplings and olefin aminofunctionalizations offer tremendous potential for sustainable, low-cost methods for selective C-C and C-N bond formation in organic synthesis, a detailed molecular-level understanding of these systems has remained elusive, thus, hindering rational catalyst development. This limitation is in stark contrast to palladium chemistry, where detailed studies of active catalyst structure and mechanism have provided the foundation for the continued design and development of catalysts with novel and/or improved catalytic performance. Our long-term goal is to develop iron-catalyzed carbon-carbon and carbon-heteroatom bond forming reactions to the level of understanding currently present for palladium, thus permitting the rational development of iron chemistry across the spectrum of desired C-C, C-N and C-X (X = B, F, etc.) bond forming reactions. In the proposed grant, a novel experimental approach combining inorganic spectroscopies, density functional theory, synthesis and kinetic studies will be utilized to provide molecular-level insight into the active iron catalysts and reaction mechanisms involved in iron- catalyzed C-C cross-coupling and olefin aminofunctionalization. These insights can be utilized to inspire and facilitate the development of new catalysts and reaction methodologies with improved catalytic performance. Following our successful work in the prior grant period, the specific aims of the proposal are to: (1) expand molecular-level understanding of the active iron catalysts and reaction mechanisms present in iron-ligand catalyzed C-C cross-coupling, (2) expand molecular-level understanding of the active iron catalysts and reaction mechanisms present in C-C cross-couplings with simple ferric salts, and (3) develop molecular-level understanding of the active iron catalysts and reaction mechanisms present in iron-catalyzed olefin aminofunctionalizations. The research is innovative because it involves a novel physical-inorganic approach to study iron-catalyzed organic reactions and advances our understanding of the active iron species and mechanisms involved in catalysis to inspire and facilitate the development of improved methodologies. The proposed research is significant because it is expected to expand the number of molecules that can be made using low-cost, sustainable iron catalysis. Long term, this expansion of synthetic methods will enable discoveries in molecular biology and pharmacology of direct impact to human health.